1. Field of the Invention
The present invention relates to standardized mechanical interface (SMIF) systems for reducing particle contamination, and more particularly to systems for transferring articles from a transportable container (e.g. a SMIF pod), which is sealable to prevent influence of external factors on the contents of the container, to a processing station, and returning articles from the processing station to the transportable container.
2. Description of the Related Art
A standardized mechanical interface (SMIF) system has been proposed by the Hewlett-Packard Company as disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of the SMIF system is to reduce particle fluxes onto articles, for example, semiconductor wafers. This end is accomplished, in part, by mechanically ensuring that during transportation and storage the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
The SMIF concept is based on the realization that a small volume of controlled (with respect to motion, air flow direction and external contaminants), particle-free air provides a clean environment for wafers. Further details of one proposed system are described in the article entitled "SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING," by Mihir Parikh and Ulrich Kaempf, Solid State Technology, Jul. 1984, pp. 111-115. SMIF systems are concerned with particle sizes which range from below 0.1 micrometers (microns) to above 200 microns. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are 1 micron and under. Unwanted contamination particles which have geometries measuring greater than 0.05 microns substantially interfere with 1 micron geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.5 microns and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafer cassettes; (2) canopies placed over cassette ports and wafer processing areas of processing equipment so that the environments inside the pods and canopies (after having clean air sources) become miniature clean spaces; and (3) a transfer mechanism to load/unload wafer cassettes from a sealed pod without contamination of the wafers in the wafer cassette from external environments.
Wafers are stored and transported in pods, and are transferred from a pod to a piece of processing equipment in the following manner. First, a pod is placed at the interface port on top of the canopy. Each pod includes a box and a box door designed to mate with doors on the interface ports of the processing equipment canopies. Then, latches release the box door and the canopy port door simultaneously; the box door and the interface port door are opened simultaneously so that particles which may have been on the external door surfaces are trapped ("sandwiched") between the box and interface port doors. A mechanical elevator lowers the two doors, with the cassette riding on top, into the canopy covered space. A manipulator picks up the cassette and places it onto the cassette port/elevator of the equipment. After processing, the reverse operation takes place.
In U.S. Pat. No. 4,724,874 a SMIF pod is disclosed in which a fitting is provided in the SMIF pod to allow fluids to be removed from or introduced to the interior region on the SMIF pod. The fitting provides communication between the interior region of the SMIF pod and the region outside the SMIF pod, and may be used, for example, to create a vacuum in the interior of the SMIF pod, to create an over-pressure in the interior region of the SMIF pod, and/or to introduce fluids (gases), such as helium, nitrogen, or other selected gases, into the interior region of the SMIF pod.
Processing stations, which receive materials to be processed from SMIF pods, may include an interior region having an atmosphere which is maintained as controlled humidity (e.g., dehumidified) air, nitrogen, argon, or another appropriate gas. In situations where the processing equipment has a controlled atmosphere, it is desirable to prevent contamination of the controlled atmosphere in the processing equipment when loading articles from a SMIF pod to the processing equipment. One mechanism for preventing such contamination is to use the SMIF pod disclosed in U.S. Pat. No. 4,724,874, and to control the environment in the interior region of the SMIF pod by the removal or introduction of appropriate gases into the SMIF pod. However, many SMIF pods currently in use do not have a facility for controlling the atmosphere in the interior of the SMIF pod once the SMIF pod is closed.
In addition, the door of a pod, which is lowered into the processing equipment in the process of transferring articles from the SMIF pod to the processing equipment has a certain volume of uncontrolled atmosphere. Accordingly, gases contained within the pod door can contaminate the controlled atmosphere of the processing equipment as the pod door is introduced into the process equipment.